One of the design goals of the New Radio (NR) for 5G wireless communication is to support operation on high frequencies (e.g., 28 GHz), where massive beamforming is needed to maintain adequate radio coverage. This has an impact on a number of system functions, including mobility procedures such as handover (HO). The HO procedure used in legacy long term evolution (LTE) (e.g., 4G wireless communication) is depicted in FIG. 1.
In legacy wireless communication systems, the user equipment (UE) has been configured with event based report triggering criteria. Once a triggering criterion has been met, the UE sends a measurement report to the source eNB (the eNB to which the UE is currently connected) via radio resource control (RRC). The measurement reporting parameters provided by the network aim to minimize both ping-pong as well as handover failures. For intra-frequency mobility this is typically achieved by configuring an A3 measurement event so that a report is triggered when a neighbour cell is found to be a few dB better than the serving cell. Due to measurement errors in bad radio conditions and due to the necessary filtering, the actual difference in signal strength may be worse than anticipated by the configured event threshold. A consequence of this is that many measurement reports and the subsequent mobility related RRC signalling are exchanged in challenging radio conditions and are hence error prone.
The mechanisms designed in LTE for mobility do not provide sufficient mechanisms for mobility in beam based systems. In particular, in a beam-based system like NR, and especially in higher frequency bands, the serving radio link to the UE may become impaired much more rapidly than in conventional LTE deployments. As the UE is moving out of the current serving beam coverage area, it may not be possible to conduct RRC signalling via the serving node to complete the HO procedure.